Project 4: An overall goal of this P50 is to evaluate the possible advantages that cochlear implants (Cl) designed to preserve acoustic hearing (Hybrid Cl) may have for potential Cl recipients. The other four projects in this grant use perceptual measures to characterize performance by different groups of study participants (adult vs children, hybrid vs bimodal vs standard Cl users). In this section the focus is on developing methods of predicting performance with a Cl that do not rely on behavioral participation by the user. The goal of the first .set of experiments is to develop and validate an evoked potential (EP) test battery that includes both peripheral (compound action potential) and central (cortical change response) measures of neural response and can be used to predict performance with a Cl. Peripheral EP measures (e.g. ECAP growth and/or channel interaction) will be used to characterize limitations in the information transfer imposed by the speech processor and the auditory nerve. Cortical EP measures, particularly those evoked in response to a change in some aspect of a complex signal (music, speech and/or ripple noise), will provide an index to the way complex signals are processed in the central auditory pathways. Both measures will be compared with performance data and a statistical path analysis model will be used to evaluate the relative contributions of the different levels of physiological processing to overall perception. This approach will be used to evaluate normal hearing and bimodal listeners as well as Hybrid and standard Cl users. These data address questions of how acoustic and electric stimulation is integrated and how EP measures can be used in clinical settings with pediatric populations. A second set of experiments uses within-subject comparisons to evaluate the effects of training in both adults and children. The studies proposed focus on determining whether changes in a cortical EP, assessed using speech and/or musical stimuli before and immediately following participation in a short-term training program, can accurately predict benefit from participation in a longer term training program.